Discharge device



Nov. 22, 1938. T. A. ELDER DISCHARGE DEVICE Filed Sept. 16, 1937 r v e wE m OE/MO t. mum s h vv/ b a a 1 Eh [I 11 n i v. a 3" Patented Nov. 22,1938 DISCHARGE DEVICE Thomas A. Elder, Scotia, N. Y., usignor to GeneralElectric Company, a corporation of New York Application September 16,1937, Serial No. 184,177

4 Claims. (Cl. 25027.5)

pool and for that reason are referred to in this application as "pooltype cathodes. It should be understood, however, that the term "pooltype, as used herein and in the appended claims, is not limited toliquid metals such as mercury but is intended to include solidsubstances which are capable of analogous use. Particular examples ofsuch solid substances include cadmium and tin.

In connection with a pool type discharge de- -vice (that is, a deviceemploying a pool type cathode) the vapor generated from the cathodematerial plays an important part in the operation of the device. Inorder to prevent arc-back or other undesirable interelectrodedischarges, it is necessary to provide some means for limiting thepressure of such vapor to a desired value. In discharge devices adaptedto handle substan- 5 tial power it is customary to accomplish thisresult either by providing a large condensation space somewhere in thedischarge envelope or by liquid cooling a large portion of the surfacearea of the envelope. The former solution tends w to produce acumbersome and unwieldy structure while the latter involves thedisadvantage of requiring the presence of a cooling liquid and of somemeans for circulating such liquid.

It is one object of the present invention to 5 provide a high capacitydischarge device of the type in question which is of compact and sturdyconstruction and in which air may he used as the cooling medium. Onefeature of the invention which contributes to the attainment of this ob-40 ject comprises enclosing the cathode material in a metal containerhaving its lateral walls in good heat-exchanging relation with aneffective heat-dissipating means and providing an anchoring elementeffective to confine the oath- 45 ode spot to a region of the cathodesurface which is closely adjacent to such walls. In this way the heatgenerated at the cathode spot is readily communicated to theheat-dissipating means.

In certain of its aspects my invention is pri- 50 marily applicable to amulti-anode device in which a cathode spot is maintained continuouslythroughout the operation of the device. In this connection it is myobject to provide means for successfully combining an enclosing envelope65 consisting mainly of metal with a pool type cathode which is indirect electrical contact with the main body of the envelope. Morespecifically. i this regard. my invention provides means for confiningthe cathode spot to the cathode surface in spite of the fact that suchsurface is electrically continuous with the walls of the dischargedevice. A feature of the invention which is important in this connectioncomprises the use of a cathode-spot-anchoring member so arranged as toprevent the cathode spot from 10 wandering to the walls of the dischargeenvelope and becoming fastened thereto.

The features of novelty which I desire to protect herein will be pointedout with particularity in the appended claims. The invention itself,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the drawing in which Fig. 1 represents a sectional view of adischarge device suitably emgo bodying the invention; Fig. 2 is a fullsection 7 taken on line 2-2 of Fig. 1; and Fig. 3 is an ir-' regularsection taken on line 3-3 of Fig. 1.

In the particular embodiment of the invention shown in Fig. l I haveillustrated an enclosing g5 envelope constituted principally ofan'elongated metal tube ill, for example, of seamless steel. This tube,which is represented as of cylindrical outline but which may obviouslyassume other configurations, is closed at its upper end by a transversemetal header ll adapted to support.

a plurality of anodes l2, suitably of graphite. Another header of acharacter to be more fully described hereinafter closes the lower end ofthe envelope and serves as a container for a pool type cathode.

Each of the anodes i2 is insulated from the main body of the envelope byan insulating ring it which also comprises an element of a pillar sealthrough which a lead-in conductor 18 may be brought into the interior ofthe envelope. In order to prevent excessive cross currents betweenanodes during the operation of the device they are separated by means ofmetallic baflies 20 interposed between them. The shielding thus efiectedis still further increased by the use of a transverse header 2| abuttingagainst thelower ends of the bailies 20 and having openings 22substantially aligned with the various anodes. Accumulation of condensedcathode material on the upper surface of the header 2| is avoided bycausing the header to slope inwardly toward the center of the envelopeand by providing a cenv tral opening 23 as an outlet for such material.

Angle irons 24 may be used to secure the. bailles 20 to one another andto the header ii.

The cathode of the discharge device may comprise a quantity of mercuryor of some material capableof analogous use located at the lower portionof the discharge envelope. This material may, if desired, fill theentire bottom of the envelope, thus being laterally confined by thewalls of the metal cylinder il. However, for reasons to be more fullyexplained in the following, I prefer to confine the active portion ofthe cathode to a cup-like metal container 25 forming the central portionof the bottom header of the envelope.

For the sake of clarity, the cathode material is not shown in thedrawing but its normal level during operation is indicated by the dottedline 28. This level may be established, for example, by means of anoverflow device comprising a small eyelet 21 projecting a predetermineddistance above the floor of the discharge device and communicating withthe exterior of the envelope through an aligned tube 28 (which is sealedoff before the device is placed in use). During fabrication anindeterminate amount of cathode material may be introduced into theenvelope through the tube It and then as much material allowed to fiowout as the position of the opening of the eyelet 21 will permit. In thisway a desired quantity of cathode material, determinable in accordancewith the length of the eyelet 21, may be deposited in the envelope.Because the upper end of the eyelet 21 may be slightly exposed duringthe operation of the device, it is desirable to cover it with aprotective coating II, for example, of a glass which is relativelyimmune to the action of the cathode spot.

In order to initiate a discharge in the device during its initialstarting period, there is provided in permanent contact with the cathodematerial a make-alive electrode 3i having a separate lead-in conductor32 which is insulated from the cathode material. The electrode ll maysuitably comprise a short tapered rod of semiconducting material havinga resistivity between about land ohms per centimeter cube. A particularexample of such a material comprises silicon carbide coatedsuperficially with iron nitrate as described and claimed in a copendingapplication of J. M. Cage, Serial No. 132,760, filed March 13, 1937, andassigned to the same assignee as the present application. For the mostsatisfactory operation, it is desirable that this electrode project asubstantial distance, on the order of one-half inch, into the cathodematerial. For this reason a cathode pool of substantial depth, asindicated, must be provided. However, by confining the cathode materialto the cup-like container 25, which has substantially a smaller diameterthan the main envelope cylinder II, the amount of such material requiredcan be kept within reasonable limits.

In order to assure stable and satisfactory operation of the dischargedevice, means must be provided for limiting the vapor pressure of thecathode material. This vapor pressure is primariiy a function oftemperature, and for this reason the problem is largely one of disposingof or limiting the heat developed in the cathode Pool.

Much of this heat is generated at the cathode spot and must ordinarilybe eliminated by conduction through the cathode material. Since cathodematerials such as mercury are of low thermal conductivity, this mode ofheat elimination is inherently inefilcient and unsatisfactory. For thisreason it is extremely dimcult, for example, to eliminate heat withsuflicient rapidity by conduction to cooling means associated with thebottom of the cathode pool. In accordance with my present invention,however, effective cooling is accomplished by confining the cathode spotto a portion of the cathode surface which is closely adjacent to aneil'ective heat dissipating means.

Referring again to the particular structure illustrated in the drawing,this is accomplished by the use of means adapted to confine the oathodespot to a region close to the lateral walls of the container and byproviding heat dissipating means in good heat-exchanging relation withsuch walls. This arrangement assures the existence of only a short heatpath through the cathode material.

The heat-dissipating means may take various forms and is, in the presentcase, exemplified as a heat radiator comprising a plurality of metalvanes 35 unitary with a circular member 36 which is secured in goodheat-exchanging relation with the outside wall of the container 25. Theradiator structure may suitably be composed of a highly conductivematerial, for ex-g, ample, copper, and may be maintained in good;thermal contact with the container 25 by an interposed filling I. ofsolder. Such solder may be applied, for example, with the dischargedevice in an inverted position; a gasket 39 of asbestos or the likebeing provided to prevent escape of liquid solder during the solderingprocess. A heavy copper plate 4| secured to the bottom surface of thecontainer 25 serves to maintain a good heat path from such surface tothe radiator structure. The heat-dissipating capacity of the radiator(and of the device as a whole) may be increased in use by subjecting wit to a forced draft of air, such air being preferably provided in anaxial direction, for example, upwardly along the length of the device.The efiiciency of this mode of cooling may be increased by surroundingthe device with a conforming enclosure adapted to confine the air streamand to increase its velocity.

The cathode spot may be confined to a region closely adjacent to thecooled wall of the container 26 by the use of cathode-spot-anchoringmeans of known character. In connection with the particular envelopestructure under consideration, one may use, for example, a ring 43 ofcathode-spot-anchoring material, such ring being in continuous contactwith the cathode material throughout its entire circumferential extentand projecting substantially above the oathode surface. Numerousmaterials may be employed for this use but I prefer to utilize arefractory metal, such as molybdenum, which has been thoroughly cleanedas by the use of an acidbath and hydrogen firing.

In connection with the use of such an anchor, I have noted that thecathode spot appears as a fine line following the intersection betweenthe anchoring member and the cathode material, the length of the-linedepending on the amount of current being drawn. In order that theanchoring member may be effective to anchor the cathode spot during thepassage of discharge currents of substantial magnitude, there may beprovided in connection with the ring ll auxiliary members I! ofanchoring material. These members are shown in the drawing as inwardlypro- Jecting radial portions secured to the interior.

circumference of the ring 43, and afford additional surfaces along whichthe cathode spot or line may extend.

From a thermal standpoint, the ideal arrangement of the ring 43 would beto have it in direct and continuous contact with the interior surface ofthe container 25. From a manufacturing standpoint, however, it isdifllcult to obtain such continuous contact without the occurrence ofsmall gaps or voids between the two parts. These gaps may be so fine aseffectively to exclude the cathode material, in which case theyconstitute an effective insulation against heat transfer. I, therefore,prefer to arrange the ring 43 so that its outer periphery. issufllciently spaced from the interior wall surface of the container topermit a thin layer of cathode material to exist between them. In theevent that mercury is to be used as the cathode material, a space ofabout 100 mils is satisfactory for this purpose. With a spacingsubstantially less than this value,-the surface tension of the mercuryis sufficient to prevent its filling the .intervening space. A furtheruseful aspect of the provision of a narrow space between the anchoringmember and the container wall lies in the effectiveness of such a spacein preventing the cathode spot from transferring itself to the wall ofthe container, even in cases where there is a tendency for the spot tobecome dislodged from the anchoring means. This effectiveness is aresult of the known tendency of a constricted space to inhibit the flowof arc current therethrough, and in the present situation to prevent thecathode spot from traveling into the constricted region on its way tothe envelope wall.

Whether the anchoring member is in direct contact with the containerwall or is slightly spaced therefrom, as shown, it is clear that only ashort heat path through the cathode mate- 'rial exists between theregion of the cathode spot and the heat dissipating means. For thisreason, eflicient and rapid heat transfer is assured and asatisfactorily low cathode temperature may be maintained by the use of aheat radiator of practical dimensions.

There is naturally some tendency for heat generated in the dischargespace above the oathode and particularly in the vicinity of the anodesl2 to be communicated to the cathode material through the metal walls ofthe envelope. This effect is minimized in the construction shown by thefact that a relatively long heat path is provided between the anodespace and the cathode container 25. One portion of the path comprises anannular transversely extending wall portion 41 associated with the lowerheader and which serves to connect the container 25 with the cylinderl0. This wall portion is preferably composed of substantially thinnermetal than the main body of the envelope and thus acts as an effectivethrottle for heat tending to flow toward the cathode pool. It is alsopossible and in some cases preferable to obtain this throttling effectby forming the annular wall portion 41 of a metal such as chrome-iron(stainless steel) which has a lower heat conductivity than the main bodyof the envelope.

In addition to the foregoing, the portion of the envelope lying betweenthe header 2| and the annular wall portion 41 is made of somewhatgreater length than would be otherwise necessary in order still furtherto decrease the heat flow from the portions of the envelope walladjacent to the anodes. This interposed envelope portion also serves toprovide a relatively cool receiving surface for cathode material whichmay be splashed from the cathode'pool by agitation thereof caused by thecathode spot. In this way the amount of vapor generated from thesplashed cathodematerial may bemaintained at a low value.

By consideration of the drawing it will be seen that my inventionprovides a discharge device which is of compact construction andconvenient shape. By virtue of the fact that the cathode container is ofless diameter than the main envelope cylinder, the radiator structureassociated therewith does not need to project materially beyond the mainconfines of the envelope. For this reason, the envelope, as viewedexternally, comprises a cylindrical structure which is of substantiallythe same diameter throughout its entire length. This is a factor ofconsiderable value in mounting the device and in assembling it withother apparatus.

While I have exemplified my invention by reference to a particularembodiment thereof, it will be understood that numerous modificationsmay be made by those skilled in the art without departing from theinvention. 1, therefore, aim in the appended claims to cover all suchmodiflcations as fall within the true spirit and scope of the foregoingdisclosure.

What I claim as new and desire to obtain by Letters Patent of the UnitedStates is:

1. A discharge device comprising an enclosing envelope consistingpredominantly of metal, anode structure within the envelope, meanselectrically continuous with the main body of the envelope providing ametallic receptacle for cathode material, a mercury pool of relativelyextensive surface area contained in the receptacle and in electricalcontact with the lateral walls thereof, a metalliccathode-spot-anchoring means effective to prevent a cathode spot fromleaving the mercury pool surface while retaining it at all times at aportion of such surface which is closely adjacent to the lateral wall ofthe receptacle, and a varied heat radiating structure in directheat-exchanging relation with the outer lateral wall surface of thereceptacle, whereby a short heat transfer path of low thermal resistanceis maintained from the cathode spot to the said radiating structure.

2. An air-cooled discharge device including the combination of anelongated metal cylinder comprising the main body of a dischargeenvelope, a first transverse metal header closing the upper end of saidcylinder, a plurality of anodes insulatingly supported from said header,a second transverse metal header closing the lower end of said cylinder,said second header including a central cup-like portion of smallerdiameter than the cylinder and an annular portion electrically andmechanically connecting the cup-like portion to the main body of theenvelope, a quantity of cathode material in said cup-like portion, acathode-spot-anchoiing body projecting above the surface of the cathodematerial and formed to retain the cathode spot at all times in a regionclosely adjacent to the inner lateral wall surface of the cup-likeportion, and a heat radiator comprising varied surfaces in goodheat-exchanging relation with the outer lateral wall surface of thecup-like portion.

3. An air-cooled discharge device including the combination of anelongated metal cylinder forming a discharge envelope, a transversemetal header fitted into and closing one end of the cylinder, an anodestructure insulatingly supported from said header, a second transversemetal header fitted into and closing the other end of the cylinder, saidsecond header including a central cup-like metal portion or smallerdiameter than the cylinder and an annular transversely extending metalportion electrically and mechanically connecting the cup-like portion tothe main body or the envelope, a quantity of cathode material in saidcup-like portion and in electrical contact with the lateral wallsthereof, means including a metallic cathode-spot-anchoring member forconfining the cathode spot to the surface of the cathode material and aheat radiator comprising vaned surfaces in good heat- A a,1s7,sss

exchanging relation with the outer wall 0! the cup-like portion, saidheat radiator being of substantially the same transverse extension asthe discharge envelope, whereby the device as a whole comprises astructure of approximately uniform diameter throughout its entirelength.

4. A discharge device according to claim 1 wherein thecathode-spot-anchoring means comprises a molybdenum ring having itscircumference slightly spaced from the lateral wall of the cathoderetaining means to permit a thin layer of mercury to exist therebetween,and thereby to assure good heat transier from the cathode spot to theheat-radiator.

THOMAS A. ELDER.

